Immobilized biocatalysts have found wide application in diverse areas including food processing, fine chemical production, biosensors, fuel cells and bioremediation. Immobilization of a biocatalyst, such as an enzyme, can confer a number of advantages relative to the free catalyst, including the ability to operate in organic solvents, recyclability and ease of removal from the process stream. Additional advantages include improvements in stability, favorable alterations in kinetic parameters and suitability for continuous production (Kennedy, “Principles of immobilization of enzymes” in Handbook of Enzyme Biotechnology, Ed. A. Wiseman, Ch 4, P.147 (1985)).
An immobilized biocatalyst refers to the combination of a biocatalyst and an insoluble support material. The nature of the association between the biocatalyst and the support material can be either covalent or non-covalent interaction. The biocatalyst can be attached to the surface of the support material, or distributed throughout the material in a homogenous fashion. The biocatalyst can also be physically entrapped within a porous gel matrix. The insoluble, or solid support may take the form of particles, powders, monoliths, gels, films, coatings and other materials. The solid support in general has a high surface area to maximize the contact of the immobilized biocatalyst with the reaction medium. Highly porous solid supports are preferred as they maximize surface area to volume of the immobilized biocatalyst.
Current methods for producing immobilized biocatalysts can be divided into 4 subcategories: (a) adsorption to a matrix such as carbon, chitin, celite and synthetic polymers, (b) crosslinking enzyme crystals and whole cells with gluteraldehyde and other agents, (c) gel entrapment in silica sol-gels, alginate and protein matrices, and (d) covalent attachment to resins and other carriers.
By immobilization, the performance of a biocatalyst is in general improved enough so as to offset the costs associated with the process or facilitate reaction conditions not possible without an immobilized biocatalyst, such as continuous processes. However, inexpensive immobilization methods often suffer from a number of drawbacks including lack of enzymatic and mechanical stability, leaching of the biocatalyst, fouling and limited catalytic efficiency. Other immobilization methods, such as silica sol-gel based procedures, require curing and drying steps that greatly increase production times (Gill, I. (2001) Chem, Mater. 13: 3404-3421).
There remains a need for a method to produce immobilized biocatalysts economically and to avoid many of the drawbacks associated with the current methods. The invention described herein provides for such methods and demonstrates the performance of the materials made thereby.